1. Field of the Invention
The present invention relates to an access network system that is connected to an existing local switch, includes a base station connected through a wireless circuit with fixed terminals such as user terminals installed in subscriber's houses, and is employed as an access network like a WLL (wireless local loop) with a function of concentrating user channels. Here, the access network refers to a network that connects the local switch of a caller with a called user, excluding the local switch and the user terminal themselves.
2. Description of Related Art
FIG. 7 is a block diagram showing a configuration of a conventional access network like a WLL. In FIG. 7, the reference numeral 1 designates a WAC (WLL Access Controller) which is the controller of a WLL; and 2 designates a base station that is connected with the WAC 1 through a trunk line 5. The reference numerals 3a-3b each designate user equipment connected with the base station 2 through a wireless circuit 4; and the reference numeral 6 designates a service node including the local switch. The reference numerals 7 each designate a subscriber line connecting the WAC 1 with the service node 6; 8a-8b each designate a user terminal connected to the user equipment; and the reference numeral 9 designates a service node interface installed in the WAC 1 for interfacing the WAC 1 to the service node 6. This configuration shows an example in which the subscriber lines 7 use analog lines.
Next, the operation of the conventional access network will be described with reference to FIG. 8, a sequence diagram illustrating the operation of the conventional access network as shown in FIG. 7, when a call request takes place from the service node 6 but the base station 2 detects a channel busy state in the access network.
First, the service node 6 issues a ringing (call request) to the WAC 1, and switches the state of the current subscriber line 7 connecting the service node 6 with the WAC 1 into an incoming call state. Receiving the ringing from the service node 6, the WAC 1 transmits a paging message to the all of the base stations 2. When each of the user equipment 3 accepts the paging from the service node 6 through the base station 2, it sends a link channel setup request back to the base station 2 to request a setup of a wireless channel. Receiving the link channel setup request from the user equipment 3, the base station 2 checks whether any idle channel is present in the wireless circuit 4. If the base station 2 cannot detect any idle channel in the wireless circuit 4, it sends back to the user equipment 3 a link channel assignment rejection response indicative of being unable to setup a wireless channel.
Even if the base station 2 detects an idle channel afterward, it cannot complete the incoming call to user equipment 3 because the base station 2 does not include any means for carrying out the call processing again. In the course of time, in response to the abandonment of the call by an originating terminal, the service node 6 switches the subscriber line 7 from the incoming call state to a normal state, and stops the paging signal. Detecting the halt of the paging signal by the service node 6, the WAC 1 releases the paging.
With such an arrangement, the conventional access network system cannot complete the call to the user equipment 3, when the service node 6 makes a call request, but the wireless circuit 4 between the base station 2 and the called user equipment 3 is busy (no idle channel is present in the wireless circuit 4), or the trunk line 5 between the WAC 1 and the base station 2 is busy. In addition, even if the base station 2 detects an idle channel afterward, it cannot complete the calling processing again, in spite of the incoming call state of the current subscriber line 7 of the service node 6, because the base station 2 does not comprise any means for carrying out the call processing subsequently. This presents a problem of increasing call loss.